The dumping of hazardous substances poses a significant threat to the environment. The U.S. Environmental Protection Agency's (EPA) Toxic Release Inventory (TRI) data show that over 18 million tons of hazardous substances covered by TRI were disposed of or released into the environment from 1998 through 2004.1 Hazardous substances are a serious safety and health problem that continues to endanger human and animal life and environmental quality. Discarded hazardous substances that are toxic, flammable, or corrosive can cause fires, explosions, and pollution of air, water, and land. Unless hazardous substances are properly treated, stored, or disposed of, they will continue to do great harm to living things that contact them, now and in the future. Because of the seriousness of the safety and health hazards related to hazardous waste operations and emergency response, the Occupational Safety and Health Administration (OSHA) issued its Hazardous Waste Operations and Emergency Response (HAZWOPER) standard to protect employees in this environment and to help them handle hazardous substances safely and effectively. The HAZWOPER standard covers all employers performing the following three general categories of work operations: Hazardous waste site cleanup operations (e.g., SUPERFUND cleanup), Operations involving hazardous waste that are conducted at treatment, storage, and disposal (TSD) facilities (e.g., landfill that accepts hazardous waste), and Emergency response operations involving hazardous substance releases (e.g., chemical spill at a manufacturing plant). This booklet provides an overview of the HAZWOPER requirements for each type of work operation and explains each section separately to provide a clearer understanding of the standard. Having this understanding enables employers to protect the health and safety of their employees in these different environments.